Losses of Biodiversity. Biodiversity loss and Protection. Early Prehistoric Extinctions. Two Main Explanations. Changes in biodiversity

Transcription

1 Losses of Biodiversity Biodiversity loss and Protection Early Prehistoric Extinctions Three main factors have promoted historical extinctions Overkill by humans Habitat loss and fragmentation Introduced species Changes in biodiversity Associated with environmental change Early Prehistoric Extinctions Periods of rapid extinction occur every million years. Some of these causes are associated with major geological events (e.g., asteroid impact in Yucatan, ca. 65 m.y.b.p.) Low extinction levels are characteristic of most of prehistory Extinctions in Recent Prehistory Late Pleistocene (50,000-10,000 y.b.p.) Australia: 86% of mammalian genera ca. 30,000-50,000 y.b.p. N. America: 33% of mammalian genera ca. 11,000 y.b.p. Africa: some losses, gains; no mass extinctions Late Holocene (last 5,000 y.) Madagascar: 7 of 17 lemur genera from 1,000-2,000 y.b.p.; elephant birds (1 tonne) New Zealand 14 of 18 spp. of large birds (mostly moas) between 900 and 225 y.b.p. Two Main Explanations Climate change Some large climate changes: e.g., N. American Pleistocene, but poor match to differing extinction times in different places Human colonization and its direct/indirect effects For most areas, the archeological records are not precise enough to match arrivals/losses In New Zealand, Maoris arrived 1100 years ago; most extinctions of large species occurred in next 900 years 1

2 Historical Examples of Overkill in North America Great auk (Alcidae) Passenger pigeon (Columbidae) Steller s sea cow (Sirenia) Great Auk - Extinct by 1857 Penguin-like flightless 10 kg seabird Islands in Atlantic: Funk Isl. Nfld., 100,000 pairs Hunted for meat, feathers, eggs The Steller s Sea Cow Passenger pigeon The most abundant large terrestrial bird in N. America in Hunting drove it to extinction. A large (ca. 5 tonne) manatee from the Bering Sea Fed on kelp (marine algae) Discovered in 1740 Hunted wastefully to extinction by traders by 1767 Habitat Destruction Factor 2: Habitat Loss and Fragmentation Habitat destruction by humans is the largest recent cause of extinctions. Two related impacts - habitat loss and habitat fragmentation. Fragmentation implies a loss of connections, and corridors that link fragments may be beneficial 2

3 Some species are strongly influenced by habitat fragmentation Area sensitive species: Do not occur in smaller fragments 100 Area-sensitive Species Woodlot size influences red squirrels in the Netherlands Percent occupied n = 4 n = 9 n = 11 Eastern Yellow Robin 0 n = 7 n = SE Australia Area of remnant (ha) Do corridors increase movement among patches? - butterfly study Checkerspot Euptoieta Claudia. Lives in open habitat within forests N. Haddad Ecol. Appl. 9: (1999) 3

4 Corridors Affect Survival and Population Growth in Fragmented Habitats Studies of the blue-breasted Fairy wren By L. & M. Brooker Wrens live in the Western Australia wheat belt only 7% of habitat left Wren Performance in Connected and Unconnected Fragments Connected Unconnected Juvenile 38% 24% Survival during dispersal Population Growth rate Not everyone agrees that fragmentation effects are generally strong. The existing literature suggests that they should be evaluated on a case-by case basis (M- A Villard et al. Ecological Applications 12 (2) 2002 Smith, J. & J. Hellmann 2002 Trends Ecol. Evol. Introduced Species Factor 3 - Introduced Species Have caused 40% of historical extinctions of mammals, fishes and birds Nile perch Lates niloticus to Lake Victoria Red foxes Vulpes fulva to Australia Brown tree snakes Boiga irregularis to Guam 4

5 Nile perch introduced to Lake Victoria in 1980s Caused extinction of 200 endemic species of cichlid fishes by 1997 (O. Seehausen et al Cons. Biology 11: ) Impacts of introduced predators Next Class Preventing loss of biodiversity Conserving Biodiversity an Hierarchical Approach Catalogue occurrences of both rare and common species thoroughly Protect multiple examples of representative ecosystems and habitats Within ecosystems, take actions to assist declining species (the Declining Population Paradigm) 5